Electrodeposition



United States Patent tion of New Jersey No Drawing. Filed Nov. 7, 1960,Ser. No. 67,497 18 Claims. (Cl. 204-55) This invention is directed tothe electrodeposition of bright zinc and more particularly to novelbrightener compositions for incorporation into cyanide baths useful inthe electrodeposition of bright zinc.

It is an object of this invention to provide an improved process forelectrodepositing bright zinc.

It is also an object of this invention to provide an improved aqueousbath for the electrodeposition of bright zinc.

It is still another object of this invention to provide novel brightenercompositions for incorporation in improved aqueous cyanide baths forelectrodepositing bright zinc.

Since about 1935, various additives have been added to aqueous cyanidezinc baths to produce bright zinc electrodeposits. Among the more widelyused additives have been a group of aromatic aldehydes includinganisaldehyde, piperonaldehyde, veratraldehyde, and2,3-dimethoxybenzaldehyde. I have now discovered that when o-vanillin(3-methoxy-2-hydroXy-benzaldehyde) is used in conjunction with at leastone of the aforelisted aldehydes as the brightener additive, theconsequent bright zinc electrodeposit is superior to any heretoforeknown. The deposits are more lustrous and glossy. It was found that itwas possible to obtain bright zinc over a wider current density rangethan heretofore possible. During the electrodeposition process, thedeposit appears to have leveling characteristics superior to those fromprior baths which have little or no leveling ability.

The electrodeposition of bright zinc from aqueous cyanide zinc solutionsusing my brightener composition is similar to the conventional processesusing similar baths which do not contain o-vanillin in conjunction withone of the four noted aldehydes. Such baths and processes are describedin Modern Electroplating, edited by A. G. Gray, The ElectrochemicalSociety, 11953, pages 460-482.

It is important that the baths be relatively free of impurities.Although my brightener composition is effective with all known brightcyanide aqueous solutions, for barrel plating I prefer to use baths andconditions as noted in Column A of Table I, and for rack plating Iprefer to use baths and conditions set forth in Column B of Table I.Conventional wetting agents, such as trimethyl- C-decyl-wbetaine, inamounts between 0.1 g./l. (gram per liter) and 1 g./l. are useful forrack plating purposes to prevent pitting and to eliminate some tendencytoward vertical striations. The use of polyvinylalcohol and/0r gelatinwith aldehydes is common in the known bright zinc baths and their use isalso preferred with my brightener combination.

The amount of my brightener combination, consisting of o-vanillintogether with at least one of the following Patented May 7, 1963aldehydes: anisaldehyde (p-methoxybenzaldehyde), piperonaldehyde(3,4-methylenedioxybenzaldehyde), veratraldehyde (3,4dimethoxybenzaldehyde), and 2,3 dimethoxybenzaldehyde, to be added tothe bath varies Widely dependent on such factors as the composition ofthe plating bath, the plating conditions, the relative proportion of theo-vanillin to the other aldehyde(s) in the brightener composition, thekind and surface of the basis metal, and the brightening effect desired.Although brightening effect is noted with amounts as small as 0.05g./l., it is preferred to use at least about 0.1 g./l. It is notcontemplated that more than about 0.5 g./l. will be utilized since inexcess of this concentration there is little increase in brightness withincreased concentration of the brightener composition. In addition, inexcess of about 0.5 g./l. the solubility of some of the aldehydes, suchas anisaldehyde, released from the bisulfite adduct, may besubstantially exceeded.

Due to the various factors noted above, the relative proportion of theo-vanillin to the other aldehyde(s) in the brightener composition mayvary widely. However, it is generally preferred that the weight ratio ofthe o-vanillin to the other aldehyde(s) be at least about 1:10 and maybe as much as 1:1. Good commercial results are obtained in the range of1:4 to 1:1 and optimum results are obtained within different portions ofthis range dependent upon the particular brightener composition.

The aldehydes generally and particularly those of interest in thepresent invention are only slowly soluble in aqueous cyanide zincelectroplating baths. The compounds per se are dissolved in such bathsslowly with agitation. It has been found that the aldehyde-bisulfiteadduct formed by the mixing and heating of the aldehyde with sodiumbisulfite in at least a 1:1 molar ratio is a convenient method ofsolubilizing aldehydes and placing them in a more convenient form forhandling. These aldehydebisulfite adducts are used in the known additionof such aldehydes as anisaldehyde to zinc electroplating baths. Insimilar manner, I have found that the combination of o-vanillin togetherwith one or more of the other specified aldehydes also is mostconveniently made in the form of the bisulfite adduct. The method ofpreparing the adduct is not critical; for a brightener combinationcontaining one part of o-vanillin to one part of anisaldehyde, theadduct could be made by physically mixing one mole of o-vanillin, onemole of anisaldehyde, and at least two moles, but preferably an excess,of sodium bisulfite; or the o-vanillin-sodium bisulfite adduct and theanisaldehyde-bisulfite adduct could be prepared separately and the twoadducts then combined to form my brightener combination. My preferredbrightener compositions contain the o-vanillin-bisulfite adduct and oneof the other four specified aldehyde-bisulfite adducts in a weight ratioof 1:4 to 1:1.

I have found that the use of between about 0.1 g./l. to about 1.0 g./l.of an animal gelatin or glue and between about 0.02 g./l. and 0.1 g./l.of a polyvinylalcohol are optimumly advantageous in the bath.

I have prepared novel and preferred compositions incorporating thevarious additives necessary for bright zinc plating in both solid'andliquid formulations. The preferred solid formulations are shown in TableI1, and the preferred liquid formulations are shown in Table III.

The solid compositions-of Table II are added to zinc baths in amountssufiicient so that the total weight of composition added is between 0.25g. and 2.5 g. to each liter of bath and preferably between 0.6 g. and1.2 g.

Table III Optimum Range, Conceng./l. tration,

total aldehyde 45-60 55. 2 animal gelatin 125-175 150 polyvinylalcohol2-5 3.82 sodium metaloisulfite (Nazsgo 45-60 55. 5

In the liquid compositions shown in Table III, the aldehydebisulfiteadduct was formed during the preparation of the liquid composition. Theliquid composition is added to the zinc plating bath in amounts between1 ml./l. of bath and ml./l., and preferably 2.5 rnL/l. of bath to 5ml./l., which is equivalent to 0.14 to 0.2 g./l. of the mixed aldehydes.

For the purpose of giving those skilled in the art a betterunderstanding of the invention, illustrative examples are given. InExamples 1 through 4 an aqueous bath containing 60 g./l. of zinccyanide, 42 g./l. of sodium cyanide, and 80 g./l. of sodium hydroxidewas used. Electroplating was carried out at 25 C. in conventional Hullcells and in other tests which simulate barrel plating conditions.

Example I.--The optimum concentration of the composition from Table IIcontaining 22.5% of anisaldehydebisulfite and 22.5 ofo-vanillin-bisulfite was used in a range of from 0.6 to 1.2 g./1. ofsolution.

Example 2.The optimum concentration of the composition from Table IIcontaining 22.5% of piperonaldehyde-bisulfite and 22.5% ofo-van-illin-bisulfite was used in a range of from 0.6 to 1.2 g./l. ofsolution.

Example 3.The optimum concentration of the composition from Table IIcontaining 22.5 of veratraldehyde-bisulfite and 22.5 ofo-vanillin-bisulrfite was used in a range of from 0.6 to 1.2 g./l. ofsolution.

Example 4.The optimum concentration of the composition from Table IIcontaining 22.5 of 2,3-dimethoxybenzaldehyde-bisulfite and 22.5% ofo-vanillin-bisulfite was used in a range of from 0. 6 to 1.2 g./l. ofsolution. The zinc electrodeposited in Examples 1-4 was bright with goodluster and gloss. Similar experiments were run utilizing instead of thenoted amounts of the two additives 45% of the bisulfite adduct of eachof the four noted additives, and a fifth experiment was run using 45% ofthe o-vanillin-bisulfite adduct. In all cases, the deposits of Examples1-4 were superior to those where only one of the aldehydes was used. Inaddition, the bath characteristics in relation to leveling and theuseful current density range were superior. The deposits with thediscovered combinations of additives were also much less yellowish incolor, which is a desirable characteristic when the use of a subsequentnitric acid or proprietary bright dip is not desired.

Example 5 .The liquid composition of Table III utilizing 11.4 g./l. ofo-van-illin and 43.8 g./l. of anisaldehyde was added to the zinc platingbath in a range of from 2.5 to 5.0 m1./l.

Example 6.The liquid composition of Table III utilizing 11.4 g./l. ofo-v-an-illin and 43.8 g./l. of piperonaldehyde was added to the zincplating bath in a range of from 2.5 to 5:0 ml./l.

Example 7.The liquid composition of Table III utilizing 11.4 g./l. ofo-vanillin and 43.8 g./ l. of veratraldehyde was added to the zincplating bath in a range of from 2.5 to 5.0 ml./l.

Example 8.The liquid composition of Table III utilizing 11.4 g./l. ofo-vanillin and 43.8 g./l. of 2,3-dimethoxybenzaldehyde was added to thezinc plat-ing bath in a range of from 2.5 to 5.0 ml./l.

In Examples 911 an aqueous bath containing 60 g./l. of zinc cyanide, 17g./l. of sodium cyanide, and g./l. of sodium hydroxide was used.

Example 9.The optimum concentration of the composition from Table IIcontaining 22.5 of anisaldehydebisulfite and 22.5 ofo-vanillin-bisulfite was used in a range of from 0.6 to 1.2 g./l. ofsolution.

Example 10.The optimum concentration of the composition from Table IIcontaining 22.5 of piperonaldehyde-bisulfite and 22.5 ofo-vanillin-bisulfite was used in a range of from 0.6 to 1.2 g./l. ofsolution.

Example .1.1.The optimum concentration of the composition of Table IIcontaining 22.5% of veratraldehydebisulfite and 22.5 ofo-vanillin-bisuliite was used in a range of from 0.6 to 1.2 g./l. ofsolution.

In Examples 12 and 13 the same zinc bath composition was used as forExamples 57 inclusive.

Example J2.-A concentration of the composition from Table II containing33.8% of anisaldehyde-bisulfite and 11.2% of o-van-illin-bisulfite wasused in a range of from 0.6 to 1.2 g./l. of solution.

Example 13.-A concentration of the composition from Table II containing30% of anisaldehyde-bisulfite and 15% of o-vanillin-bisulfite was usedin a range of from 0.6 to 1.2 g./l. of solution.

In Examples 9-13 inclusive utilizing a zinc bath having a NaCN to Znratio of 2.0 all the advantages realized in Examples 1-8 (NaCN to Znratio of 2.74) inclusive were realized. In addition, for the bathshaving a NaCN to Zn ratio of 2.0 there seemed a lesser tendency towardvertical striations obtained in rack plating, thus permitting operationwith little or no cationic surface active agent.

In Examples 14 and 15 the same zinc bath composition was used as forExamples 9-13.

Example 14.--The liquid composition of Table III utilizing 20 g./l. ofo-vanillin and 35.2 g./l. of anisaldehyde was added to the zinc platingbath in a range of from 2.5 to 5.0 ml./l.

Example 15.The liquid composition of Table III utilizing 5.2 g./l. ofo-vanillin and 50 g./l. of anisaldehyde was added to the zinc platingbath in a range of from 2.5 to 5:0 ml./l.

In Examples 16 and 17 the same zinc bath composition was used as forExamples 1-8.

Example I6.The liquid composition of Table III utilizing 20 g./l. ofo-vanillin and 35.2 g./l. of anisaldehyde was added to the zinc platingbath in a range of from 2.5 to 5.0 ml./l.

Example 17.-The liquid composition of Table III utilizing 5.2 g./l.o-vanillin and 50 g./1. of anisaldehyde was added to the zinc platingbath in a range of from 2.5 to 5 .0 ml./l.

In Examples 14-17, there were realized all the advantages enumerated forExamples 1-13. Again it was noted in Examples 14 and 15 that the lowerNaCN to zinc ratio of 2.0 reduced the tendency toward deposit striationin rack plating.

As is Well known in the prior art, other tests where the zinc metalconcentration was varied keeping the NaCN to Zn ratio within thepreferred limits, showed only an effect in increasing or decreasing thelimiting current density with increasing or decreasing zinc metalconcentration.

Similar experiments were run utilizing instead of the noted combinationof the two aldehydes only one aldehyde in an amount equal to the totalo-vanillin-aldehyde combination. In turn, each of the five aldehydes wasutilized separately. In all cases, the results were inferior to thoseobtained in Examples 5-17 in the same respects as those discussedhereinbefore regarding the superiority of Examples 1-4.

In .addition to the advantages of process and deposit obtained utilizingthe o-vanillin-aldehyde combination noted hereinbefore, I find that myas plated bright zinc may be brought to a superlative luster andappearance resembling bright chromium, heretofore unattainable, bytreatment with a nitric acid or one of the bright zinc proprietary dips.

Another advantage is based on the finding that ovanillin imparts astrong yellow color to the electro-plating solution which is a basis fora simple analytical technique based on colorimetric measurements. Theo-vanillincontaining brighteners have also been found to be long lastingand unusually stable at the conventional zinc plating temperatures. Theyare also stable at plating temperatures up to as high .as about 50 (3.,whereas the usual brighteners suffer more rapid breakdown attemperatures above about 35 or 40 C. Zinc is usually electro-depositeddirectly on various iron and steel alloys, although it may beelectrodeposited on other basis metals as well.

As many embodiments of this invention may be made without departingfrom'the spirit and scope thereof, it is to be understood that theinvention includes all such modifications and variations as come withinthe scope of the appended claims.

I claim:

1. A process for electroplating bright, lustrous zinc comprisingelectrodepositing zinc from an aqueous alkali cyanide bath containingzinc ions and containing at least 0.05 g./l. of total aldehyde, saidtotal aldehyde consisting essentially of o-vanillin and at least onecompound selected from the class consisting of anisaldehyde,piperonaldehyde, veratraldehyde, and 2,3-dimethoxybenzaldehyde, theweight ratio of said o-vanillin to said compound being between 1:10 and1:1.

2. A process for electroplating bright, lustrous zinc comprisingelectrodepositing zinc from an aqueous alkali cyanide bath containingzinc ions and containing between 0.05 g./l. and 0.5 g./l. of totalaldehyde, said total aldehyde consisting essentially of o-vanillin andat least one compound selected from the class consisting ofanisaldehyde, piperonaldehyde, veratraldehyde, and2,3-dimethoxybenzaldehyde, the weight ratio of said o-vanillin to saidcompound being between 1:10 and 1:1.

3. A process for electroplating bright, lustrous zinc comprisingelectrodepositing zinc from an aqueous alkali cyanide bath containingzinc ions and containing between 0.1 g./l. and 0.5 g./l. of totalaldehyde, said aldehyde consisting essentially of o-vanillin and atleast one compound selected from the class consisting of anisaldehyde,piperonaldehyde, veratraldehyde, and 2,3-dimethoxybenzaldehyde, theweight ratio of said o-vanillin to said compound being between 1:4 and1:1.

4. An aqueous alkali cyanide bath containing zinc ions for theelectrodeposition of bright and lustrous zinc and containing as thebrightening additives at least about 0.05 g./l. of total aldehyde, saidtotal aldehyde consisting essentially of o-vanillin and at least onecompound selected from the class consisting of anisaldehyde,piperonaldehyde, veratraldehyde, and 2,3-dimethoxybenzaldehyde, theratio weight of said o-vanillin to said compound being between 1:10 and1:1.

5. An aqueous alkali cyanide bath containing zinc ions for theelectrodeposition of bright and lustrous zinc and containing as thebrightening additives between 0.1 g./l. and 0.5 g./l. of total aldehyde,said total aldehyde consisting essentially of o-vanillin and at leastone compound selected from the class consisting of anisaldehyde,piperonaldehyde, veratraldehyde, and 2,3-dimethoxybenzaldehyde, theweight ratio of said o-vanillin to said compound being between 1:4 and1:1.

6. The bath of claim 5 in which the total aldehyde consists essentiallyof o-vanillin and anisaldehyde.

7. The bath of claim 5 in which the total aldehyde consists essentiallyof o-vanillin and piperona'ldehyde.

8. The bath of claim 5 in which the total aldehyde consists essentiallyof o-vanillin and veratraldehyde.

9. The bath of claim 5 in 'which the total aldehyde consists essentiallyof o-vanillin and 2,3-dimethoxybenzaldehyde.

10. An aqueous alkali cyanide bath containing zinc ions for theelectrodeposition of bright and lustrous zinc and containing as thebrightening additive o-vanillin and at least one compound selected fromthe class consisting of anisaldehyde, piperonaldehyde, veratraldehyde,and 2,3-dimethoxybenzaldehyde, the weight ratio of the ovanillin to theother aldehyde being between 1:10 and 1:1; said brightener additivesbeing added to said bath in the form of their bisulfite adducts and inan amount suflicient so that the bath contains between 0.1 g./l. and 0.5g./l. of total aldehyde.

11. The bath of claim 10 in which the weight ratio of o-vanillin to theother aldehyde is between 1:4 and 1:1.

12. The bath of claim 10 in which the brightener additives are added ina composition which also contains animal gelatin and polyvinylalcohol.

13. A composition of matter for making up and for maintaining aqueousalkali cyanide zinc electroplating baths consisting essentially of analdehyde-bisulfite adduct, said aldehyde-bisulfite adduct comprising (1)o-vanillin and (2) at least one aldehyde selected from the classconsisting of anisaldehyde, piperonaldehyde, veratraldehyde, and2,3-dimethoxybenzaldehyde, and (3) sodium bisulfite, the said sodiumbisulfite being present in an amount equal to at least a 1:1 molar ratiowith the total aldehyde, and the weight ratio of o-vanillin to the otheraldehyde being between 1:10 and 1:1.

14. A composition of matter for making up and for maintaining aqueousalkali cyanide zinc electroplating baths consisting essentially of40%-50% aldehyde-bisulfite adduct, 10%15% animal gelatin, 5 %10%polyvinylalcohol, and the balance sodium sulfate; saidaldehyde-bisulfite adduct comprising (1) o-vanillin and (2) at least onealdehyde selected from the class consisting of anisaldehyde,piperonaldehyde, veratraldehyde, and 2,3- dimethoxybenzaldehyde, theweight ratio of the o-vanillin to the other aldehyde being between 1:10and 1:1, and (3) sodium bisulfite, the said sodium bisulfite beingpresent in an amount equal to at least a 1:1 molar ratio with the totalaldehyde.

15. The composition of claim 14 in which the weight ratio of o-vanillinto the other aldehyde is between 1:4 and 1:1.

16. An aqueous composition of matter for making up and for maintainingaqueous alkali cyanide zinc electroplating baths consisting essentiallyof 45 g./l. to 60 g./l. of total aldehyde, and 45 g./l. to 60 g./l. ofsodium meta- -bisulfite; the total aldehyde consisting of o-vanillin andat least one aldehyde selected from the clas s consisting ofanisaldehyde, piperonaldehyde, veratraldehyde, and2,3-dimethoxybenzaldehyde, the weight ratio of o-vanillin to said otheraldehyde being between 1:10 and 1:1.

17. An aqueous composition of matter for making up and for maintainingaqueous alkali cyanide zinc electroplating baths consisting essentiallyof 45 g./l. to 60 g./-l. of total aldehyde, g./l. to g./l. of animalgelatin, 2 g./1. to 5 g./l. of polyvinyl'alcohol, and 45 g./1. to 60g./l. of sodium metabisulfite; the total aldehyde consisting ofo-vanillin and at least one aldehyde selected from the class consistingof anisaldehyde, piperonaldehyde, veratraldehyde, and2,3-dimethoxybenzaldehyde, the weight ratio of o-vanillin to said otheraldehyde being between 1:10 and 1:1.

18. An aqueous composition of matter for making up and for maintainingaqueous alkali cyanide zinc electroplating baths consisting essentiallyof 45 g./l. to 60 g./l. of total aldehyde, 125 g./1. to- 175 g./l. ofanimal gelatin,

7 2 g./l. to 5 g./l. of polyvinylalcohol, and 45 g./l. to 60 g./1. ofsodium metabisulfite; the total aldehyde consisting of o-Vanillin and atleast one aldehyde selected from 'the class consisting of anisaldehyde,piperonaldehyde,

veratraldehyde, and 2,3-dimethoxybenzaldehyde, the Weight ratio ofo-vanillin to said other aldehyde being between 1:4 and 1:1.

References Cited in .the file of this patent UNITED STAT-ES PATENTSHoflman Apr. 3, 1956 FOREIGN PATENTS France Nov. 18, 1953

1. A PROCESS FOR ELECTROPLATING BRIGHT, LUSTROUS ZINC COMPRISINGELECTRODEPOSITING ZINC FROM AN AQUEOUS ALKALI CYANIDE BATH CONTAININGZINC IONS AND CONTAINING AT LEAST 0.05 G./1. OF TOTAL ALDEHYDE, SAIDTOTAL ALDEHYDE CONSISTING ESSENTIALLY OF O-VANILLIN AND AT LEAST ONECOMPOUND SELECTED FROM THE CLASS CONSISTING OF ANISALDEHYDE,PIPERONALDEHYDE, VERATRALDEHYDE, AND 2,3-DIMETHOXYBENZALDEHYDE, THEWEIGHT RATIO OF SAID O-VANILLIN TO SAID COMPOUND BEING BETWEEN 1:10 AND1:1.